1. Field of the Invention
The present invention relates to a horizontal rotary hook of a sewing machine that can have an extremely simple configuration and includes a configuration in which a permanent magnet for disposing, in an outer rotary hook, an inner rotary hook having a metal plate in a bottom portion is fixed to a bottom portion of the outer rotary hook.
2. Description of the Related Art
Generally, sewing machines include a horizontal rotary hook device accommodating a bobbin. The horizontal hook device includes outer and inner rotary hooks. A gear shaft is integrally attached to a lower end surface of the outer rotary hook. A gear is fixedly mounted to a lower shaft and meshes with the gear shaft. Thus, the outer rotary hook rotates along with the rotation of the lower shaft. The inner rotary hook accommodated in the outer rotary hook might make random movement such as oscillation during a sewing operation. Such random movement of the inner rotary hook causes noise and affects sewing performance. Japanese Patent Application Laid-open No. 2006-94905 discloses a specific configuration for addressing this problem. Specifically, the configuration is one of various configurations in which a magnet is used to prevent the inner rotary hook accommodated in the outer rotary hook from floating during the sewing operation.
Japanese Patent Application Laid-open No. 2006-94905 can achieve a state where the inner rotary hook in the outer rotary hook is extremely stable, and thus can solve various problems attributable to the random movement of the inner rotary hook. The outer rotary hook may be made of a metal material as a magnetic material, so that the configuration where the inner rotary hook is magnetically attracted to be fixed is easily achieved. However, in recent years, the outer rotary hook has been made of a synthetic resin material as a non-magnetic material in many cases for the sake of cost and the like. Thus, the magnet is fixedly attached to the bottom surface of the outer rotary hook made of the synthetic resin with an adhesive, an adhesive tape, and the like.
When the adhesive or the adhesive tape is used for the fixing, contact surfaces of the inner rotary hook and the magnet need to be cleaned so that the magnet and the inner rotary hook favorably adhere to each other, the bottom surface of the outer rotary hook needs to be cleaned, and even a degreasing treatment is required to remove oil. The adhesiveness of the adhesive is low unless such treatments are sufficiently performed. Thus, the magnet is likely to be detached from the bottom surface of the outer rotary hook while the sewing machine is under operation. However, the cleaning of the bottom surface of the outer rotary hook and the removal of oil (degreasing treatment) require additional cumbersome operation steps which in turn complicate an assembling operation.
Thus, in the configuration of Japanese Patent Application Laid-open No. 2006-94905, a yoke member formed of a magnetic body is mounted to a bottom portion of the outer rotary hook, and a magnet piece is fixedly attached to the yoke member. The yoke member has a form of a plate, and includes a circular circumferential wall. The circumferential wall is not continuously formed in the circumferential direction. The circumferential wall is partially notched at an equal interval to form a plurality of protrusions that engage with ribs of the outer rotary hook. Thus, the yoke member can be fixed in a stable state, without rotating without the outer rotary hook (see FIG. 4A).
Unfortunately, in this configuration, a needle thread n of the bobbin is likely to be caught by the notches in the circumferential wall, defined by the protrusions of the yoke member or an engaging portion between the protrusions and the ribs (see FIG. 4B), to hamper the sewing operation of the sewing machine (see FIG. 4). Furthermore, to form the protrusions and the like on the yoke member, steps for manufacturing the yoke member are increased and even a unit price of the yoke member might be increased.
Furthermore, forming the notches in the circumferential wall of the yoke member further rises the problem that strong magnetic force of a magnet piece disposed in the yoke member cannot be achieved. A technical goal (object) achieved by the present invention is to fix a fixing holder, for fixing the permanent magnet, stably to the outer rotary hook and prevent a thread extending from the bobbin from being caught in the hook, with an extremely simple configuration that does not use a plurality of protrusions as a rotation stopper.